1. Field of the Invention
This invention relates to foundry molding compositions and, more particularly, to foundry moulding compositions which do not evolve pungent acid gases on thermal decomposition. The invention also comprises a process for the production of foundry moulds and cores using said compositions.
2. The Prior Art
Phenol-formaldehyde (PF), phenol-formaldehyde/furfuryl alcohol (PF/FA), urea-formaldehyde/furfuryl alcohol (UF/FA) and furfuryl alcohol-formaldehyde condensation products catalysed with strong acid catalysts, such as phosphoric acid, sulphuric acid and paratoluene sulphonic acid and the like, are well known as binders for sand in the production of cold-setting foundry moulds and cores. Aromatic sulphonic acids are more commonly employed than all other types but have the disadvantage that pungent fumes of sulphur dioxide are evolved on thermal decomposition.
UF/FA condensation products contain nitrogen which can form ammonia on thermal decomposition and this tends to neutralize the sulphur dioxide. However, nitrogen in the binder can react with certain metals, such as, for example, grey and nodular irons and steel, resulting in the formation of small bubbles in the final casting, a defect known in the foundry industry as "pinholing". The employment of UF/FA binders is consequently restricted.
Phosphoric acid may be employed as a catalyst but tends to build up on the sand on repeated attrition reclamation and this reduces the refractoriness of the sand. Phosphoric acid is also incompatible with PF/FA condensation products and, as a result, the moulds and cores produced exhibit poor bond strengths.
U.S. Pat. No. 3,599,433 to Murata et al issued on Aug. 17, 1971 describes a system for soil stabilization consisting of a highly alkaline resole cross-linked with lactone. German DAS No. 1065605 to B.A.S.F. shows curing of phenol-formaldehyde condensates with lactones.